Subject: H-Bonds and Homo

From: [email-masked] (Kamal Azzaoui)
Date: Thu, 01 Jun 1995 09:37:12 +0100

Hi

Some days ago I asked this question :

I would like to know if somebody had any references about relationships
between HOMO or LUMO energy level and H-bond acceptor or donor parameters.

I received one answer from Tim Mitchell, his paper is interesting

thanks Tim

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Well,  you could think of this as H-bonding.......   I reported the 
relationship between pKa and HOMO energy in Eur J Med Chem 1990, 25, 117-120.  
If a base (imidazolidine in this case) is to accept a proton, it must form the 
covalent bond by transfering charge from it's lone pair.  The easier it can do 
this, the more likely it is to happen, hence the effect on pKa.  Most often the 
lone pair orbital makes up a large part of the HOMO, hence the relationship 
between pKa and E  HOMO. As least that's what we were proposing....

If you think of H-bonding as some part-way state to protonation, then you may 
find a relationship between E HOMO and H-bond acceptor ability.  Please let me 
know your findings.....

Tim Mitchell  SmithKline Beecham, Broockham Park, UK.

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        Kamal AZZAOUI     

   LCBA. Universite d'Orleans.
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